Frequently Asked Questions

Last updated: 2021-04-07


Question. I am making a three-layer mask, outer layers cotton, middle polypropylene, using a 3D mask design, with a nosewire for good fit. We find it breathable. Should we still be wearing two masks?

Answer. We don't have comparative data for different mask designs but subjectively, the 3D masks we have seen fit well with minimal leak, unless made with a low-breathability fabric such as batik. Your mask meets the criteria of a good mask. We do not think you need more layers than this. We would also caution against wearing two 3D masks because they often don't stack well, and anything that affects fit also affects effective whole-mask filtration. 


Question. Are ties or elastic over the head better than earloops?


Answer. There is limited evidence to support the use of ties rather than earloops in improving the overall efficiency of a mask. We think this is because the improved stability of the mask and tension against the face improves fit and reduces edge leak. We think adjustable over-the-head elastic is likely to be as good as ties; we recognize this is an uncommon design.  Many people prefer not to have ties over the head because of the interference with hair. People who wear head coverings such as turbans may require longer ties. If your mask has earloops, there is limited evidence that wearing it looped over the ear and also on an earguard at the nape of the neck improves overall efficiency. Finally, wearing a mask with earloops on buttons on a band or hat can improve comfort and possibly fit, but anecdotally we think that the button position may need to be individualized so that the mask is pulled backwards onto the face and not upwards.


Question. What is the role of the nose wire?


Answer. A strong long nose wire that holds position well is an intuitive choice for improving the seal at the top of the mask. Gardening or electrical wire can be used, or custom strips purchased (though these tend to be shorter that we think likely to be optimal). Based on design principles, we think coffee bag ties may be a good choice: they can be cut to custom length, are strong, wide and hold position well when bent to conform to the shape of the wearer's nose. There is limited evidence that a nose wire improves the overall filtration efficiency of a mask.


Bend the nose wire into approximate position before donning the mask. This makes it easier to make small adjustments on the face.


It is possible that some good designs fit well without a nosewire.


Question. How can I reduce glasses fog?


Answer. The first step is a good nose wire (see FAQ on nose wire), based on design principles and limited evidence from a laboratory setting. Anecdotally, we have found that the 3D design may be good for reducing fogging. Finally, consider a mask brace - a silicone or rubber device that fits over the mask to improve the seal, reduce edge leak and improve the overall filtration efficiency of a mask. There is published and preprint evidence that these devices do increase mask filtration efficiency. Mask braces are not designed to be worn over structured masks, such as the 3D mask; they are designed to work with pleated or Olson masks or disposable masks, including certified Level 1 and 3 masks issued to health care workers. They are not needed with well-fitting N95s issued to health care workers.


If you are a health care worker who needs to wear glasses, and you work in a high-risk setting and have the resources, prescription goggles worn above a mask will also afford eye protection and eliminate glasses fog. Eye protection has been found to be protective in a study that summarized previous studies (a meta-analysis). Most of the included studies were of health care workers. They were observations of what happened in those who did and didn't wear eye protection, rather than true experiments, but the effect was consistent and large.


Taping the top of the mask to the face with paper tape completely eliminates glasses fog, in anecdotal experience, and is very likely to improve fit. However, bruising and skin damage can occur when the tape is removed.